(592a) Composite Hydrogels with a Thermally-Activated Component

Mechanically robust, stimuli-responsive hydrogels have recently become a popular area of research. Work performed by Gong and co-workers has inspired a family of novel multi-network hydrogels featuring stimuli-activated high strength, such as temperature and pH. Here, we present a thermo-responsive system consisting of alginate, a natural biopolymer derived from algae, and Pluronic® F127 (F127), a synthetic triblock copolymer. These materials are widely used for drug delivery and tissue engineering applications. Alginate forms hydrogels due to “ionic crosslinking” with divalent cations, such as calcium or barium. Pluronic® solutions create thermo-reversible gels at a critical gelation temperature due to interactions between micelles. Creating a dual-component system with alginate and F127 allows for tunable control over hydrogel thermo-mechanical properties. Rheology and small-angle neutron scattering (SANS) results indicate the incorporation of F127 within an existing alginate network creates a composite hydrogel with unique temperature-dependent mechanical properties. Shear rheology and compression show a dramatic increase in modulus as the lower gelation temperature (LGT) is reached, demonstrating the “activation” of the secondary F127 gel structure within the alginate matrix. The temperature at which the F127 gels is concentration dependent. We show the effect of the gelled F127 has on the compression behavior of the composite gel, where below the LGT the native elastic response is observed, and as the LGT is reached, the response transitions into plastic deformation behavior due to the cubically packed F127 micelles sliding. Fracture analysis shows increases of up to 200% in fracture stress (e.g., from 50 kPa to 250 kPa for 3 wt% alginate/20 wt% F127) when comparing composite gels below and above the LGT, which corresponds to a nearly 600% increase over a neat alginate hydrogel.